Communication terminal apparatus and base station apparatus

ABSTRACT

An allocation section  101  in a base station apparatus of the present invention sets the transmission rate of a transmit signal for a communication terminal apparatus based on a DRC signal transmitted from that communication terminal apparatus. A power margin information detector  117  detects power margin information from a demodulated signal generated by a demodulator  115 , and, using that power margin information, a power setting section  118  makes a setting so as to give the minimum transmission power value at which received signal characteristics in each communication terminal apparatus meet the desired quality. Using the set transmission power value, the base station apparatus transmits a transmit signal of the set transmission rate to a communication terminal apparatus. By this means it is possible to suppress interference to a communication terminal apparatus that performs adaptive modulation communication with another base station apparatus and a communication terminal apparatus that performs adaptive modulation communication with the local base station apparatus at the same time.

This is a divisional of application Ser. No. 10/322,425 filed Dec. 19,2002, which is a continuation of application Ser. No. 10/069,267 filedFeb. 25, 2002.

TECHNICAL FIELD

The present invention relates to a base station apparatus andcommunication method to be used in a cellular communication system.

BACKGROUND ART

In a cellular communication system, one base station performs radiocommunication with a plurality of communication terminalssimultaneously. In such a cellular communication system, there is ademand for transmission efficiency to be increased.

As a method of increasing the transmission efficiency over the downlinkfrom a base station to a communication terminal, a method is proposed ofperforming scheduling that for allocating communication resources tocommunication terminals by means of time division, and of furthersetting a transmission rate for each communication terminal according tocommunication quality to transmit data. Hereinafter, this method isreferred to as “adaptive modulation communication”.

Adaptive modulation communication will be described below using FIG. 1.In FIG. 1, it is assumed that a base station 11 is currently performingcommunication with communication terminals 12 through 14, which arewithin the cell area 15 covered by this base station 11. Communicationterminals 20 through 22 are within the range of the cell area 15, butperform communication with a base station (not shown) other than thisbase station 11.

First, the base station 11 transmits a pilot signal to communicationterminals 12 through 14. Each of communication terminals 12 through 14estimates communication quality according to a CIR (Carrier toInterference Ratio) etc., using the pilot signal transmitted from thebase station 11, and calculates a transmission rate at whichcommunication is possible. Also, based on the transmission rate at whichcommunication is possible, each of communication terminals 12 through 14selects a communication mode indicating a combination of packet length,error correction, and modulation method, and transmits a signalindicating the communication mode to the base station 11.

Based on the communication mode selected by each of communicationterminals 12 through 14, the base station 11 performs scheduling, sets atransmission rate for each communication terminal, and notifies a signalindicating communication resource allocation to each of communicationterminals 12 through 14 via a control channel.

The base station 11 transmits data only to the relevant communicationterminal in its assigned time via a data channel. For example, when timet1 is assigned to communication terminal 12, in time t1 the base station11 transmits data only to communication terminal 12, and does nottransmit to communication terminals 13 and 14. Also, transmission powerwhen the base station 11 transmits data to communication terminals 12through 14 is always constant.

Parallel to adaptive modulation communication, ordinary CDMA (CodeDivision Multiple Access) communication is performed in parallel betweenthe base station 11 and communication terminals 12 through 14 in adifferent band from that for adaptive modulation communication.

However, in above-described conventional adaptive modulationcommunications, the following problem arises. Referring again to FIG. 1,the base station 11 transmits data to each of communication terminals 12through 14 always using fixed power, regardless of the distances tocommunication terminals 12 through 14. This power is high enough toensure that reception quality is sufficiently good at all communicationterminals in the cell area 15.

Consequently, there is a possibility that, among communication terminalsperforming adaptive modulation communication with a base station otherthan base station 11 (hereinafter referred to as “another basestation”), communication terminals within the cell area 15 covered bybase station 11 (in FIG. 1, communication terminals 20 through 22) mayreceive interference due to a signal transmitted to any one ofcommunication terminals 12 through 14 from base station 11. As a result,the communication quality of a communication terminal receivinginterference in this way will deteriorate.

For example, if the time when base station 11 transmits data tocommunication terminal 12 via a data channel is coincident with the timewhen another base station transmits data to communication terminal 20via a data channel, communication terminal 20 receives interference dueto the signal transmitted from base station 11 to communication terminal12.

Also, if base station 11 transmits adaptively modulated signals to aplurality of communication terminals (for example, communicationterminals 12 through 14) at the same time, the communication quality ofthat plurality of communication terminals will deteriorate becausedelayed waves of the signals transmitted to that plurality ofcommunication terminals will cause mutual interference.

As explained above, in above-described conventional adaptive modulationcommunications there is a problem in that an adaptively modulated signaltransmitted from a base station causes interference with a communicationterminal performing adaptive modulation communication with another basestation, or with a communication terminal performing communication withthe same base station at the same time.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a base stationapparatus and communication method that suppress interference to acommunication terminal performing communication with another basestation apparatus or a communication terminal apparatus performingcommunication with the same station at the same time.

This object is achieved by having this base station apparatus set thetransmission rate of a communication terminal apparatus based on thereception quality of that communication terminal apparatus, and performtransmission to that communication terminal apparatus using a minimumtransmission power value at which the characteristics of a receivedsignal in that communication terminal apparatus meet a desired quality.Also, the above object is achieved by having this base station apparatusset a transmission power value according to whether or not receptionquality in a communication terminal apparatus is excessive, andperforming transmission to that communication terminal apparatus usingthat transmission power value.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating conventional adaptive modulationcommunication;

FIG. 2 is a block diagram showing the configuration of a base stationapparatus according to Embodiment 1 of the present invention;

FIG. 3 is a block diagram showing the configuration of a communicationterminal apparatus according to Embodiment 1 of the present invention;

FIG. 4 is a diagram showing the method of transmission ratedetermination by the requested modulation method determination sectionof a communication terminal apparatus according to Embodiment 1 of thepresent invention;

FIG. 5 is a diagram showing how a communication terminal apparatus andbase station apparatus according to Embodiment 1 of the presentinvention perform adaptive modulation communication;

FIG. 6 is a block diagram showing the configuration of a communicationterminal apparatus according to Embodiment 2 of the present invention;

FIG. 7 is a block diagram showing the configuration of a base stationapparatus according to Embodiment 2 of the present invention;

FIG. 8 is a diagram showing an example of a DRC table used by acommunication terminal apparatus according to Embodiment 2 of thepresent invention;

FIG. 9 is a block diagram showing the configuration of a base stationapparatus according to Embodiment 3 of the present invention;

FIG. 10 is a flowchart showing the operation of a base station apparatusaccording to Embodiment 3 of the present invention;

FIG. 11 is a block diagram showing the configuration of a base stationapparatus according to Embodiment 4 of the present invention;

FIG. 12 is a flowchart showing the operation of a base station apparatusaccording to Embodiment 4 of the present invention;

FIG. 13 is a block diagram showing the configuration of a communicationterminal apparatus according to Embodiment 5 of the present invention;

FIG. 14 is a diagram showing an example of a DRC signal used by acommunication terminal apparatus according to Embodiment 5 of thepresent invention;

FIG. 15 is a block diagram showing the configuration of a base stationapparatus according to Embodiment 5 of the present invention;

FIG. 16 is a flowchart showing the operation of a base station apparatusaccording to Embodiment 5 of the present invention;

FIG. 17 is a block diagram showing the configuration of a base stationapparatus according to Embodiment 6 of the present invention;

FIG. 18 is a flowchart showing the operation of a base station apparatusaccording to Embodiment 6 of the present invention;

FIG. 19A is a diagram illustrating conceptually a first example of thedistribution of DRC values reported by a communication terminalapparatus according to Embodiment 7 of the present invention;

FIG. 19B is a diagram illustrating conceptually a second example of thedistribution of DRC values reported by a communication terminalapparatus according to Embodiment 7 of the present invention;

FIG. 20 is a flowchart showing the operation of a base station apparatusaccording to Embodiment 7 of the present invention;

FIG. 21 is a diagram showing an example of the relationship betweenaverage DRC values, dispersion, and transmission power values in a basestation apparatus according to Embodiment 8 of the present invention;and

FIG. 22 is a flowchart showing the operation of a base station apparatusaccording to Embodiment 8 of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference now to the accompanying drawings, embodiments of thepresent invention will be explained in detail below. In the followingembodiments, a base station apparatus performs “adaptive modulationcommunication” whereby data is transmitted after communication resourcesare allocated to communication terminal apparatuses by means of timedivision and a transmission rate is set for each communication terminalapparatus. A pilot signal is transmitted from the base station apparatusto a communication terminal apparatus via a control channel, and data(speech, packet, etc.) is transmitted from the base station apparatus toa communication terminal apparatus via a data channel. Signalscommunicated via the control channel and data channel are designated“control channel signal” and “data channel signal”, respectively.

Embodiment 1

FIG. 2 is a block diagram showing the configuration of a base stationapparatus according to Embodiment 1 of the present invention

In FIG. 2, an allocation section 101 ascertains a transmission rate atwhich communication is possible for each communication terminalapparatus based on a data rate control (hereinafter referred to as“DRC”) signal detected by a DRC signal detector 116 described laterherein, determines communication resource allocation to eachcommunication terminal apparatus, and gives an instruction for output ofdownlink transmit data to a buffer 102. This DRC signal is a signalindicating a transmission rate at which reception is possible by acommunication terminal apparatus at the desired quality. A detaileddescription of this DRC signal will be given later herein.

The allocation section 101 also indicates the downlink transmit datacoding method to an adaptive coding section 103, indicates the downlinktransmit data modulation method to an adaptive modulator 104, andindicates a spreading code by which downlink transmit data is to bemultiplied to an adaptive spreader 105.

The buffer 102 holds downlink transmit data, and outputs downlinktransmit data for a predetermined communication terminal apparatus tothe adaptive coding section 103 in accordance with an instruction fromthe allocation section 101. In accordance with an instruction from theallocation section 101, the adaptive coding section 103 performs codingon transmit data from the buffer 102, and outputs the coded transmitdata to the adaptive modulator 104.

In accordance with an instruction from the allocation section 101, theadaptive modulator 104 modulates transmit data coded by the adaptivecoding section 103, and outputs the modulated transmit data to theadaptive spreader 105. In accordance with an instruction from theallocation section 101, the adaptive spreader 105 spreads transmit datamodulated by the adaptive modulator 104, and outputs the spread transmitdata to a multiplexer 108.

Meanwhile a modulator 106 modulates a pilot signal and outputs themodulated pilot signal to a spreader 107. The spreader 107 spreadsmodulated pilot signal by modulator 106 and outputs the resulting signalto the multiplexr 108.

The multiplexer 108 performs time multiplexing of spread downlinktransmit data and a spread pilot signal to generate a transmit signal,and outputs the generated transmit signal to a power controller 109. Atthe start of communication, only a pilot signal is output from themultiplexer 108 to the power controller 109.

The power controller 109 amplifies the transmit signal generated by themultiplexer 108 so as to be at the transmission power value set by apower setting section 118 described later herein, and outputs theamplified transmit signal to a transmitting RF section 110.

The transmitting RF section 110 converts the frequency of the transmitsignal amplified by the power controller 109 to a radio frequency, andoutputs this signal to a duplexer 111. The duplexer 111 transmits thetransmit signal converted to a radio frequency by the transmitting RFsection 110 to a communication terminal apparatus via an antenna 112.The duplexer 111 also outputs a signal transmitted by a communicationterminal apparatus and received via the antenna 112 (received signal) toa receiving RF section 113.

The receiving RF section 113 converts the frequency of a received signalfrom the duplexer 111 to baseband, and outputs the received signalconverted to baseband to a despreader 114. The despreader 114 despreadsthe received signal converted to a baseband signal and outputs theresulting signal to a demodulator 115. The demodulator 115 demodulatesthe received signal despread by the despreader 114 to generate ademodulated signal, and outputs the generated demodulated signal to theDRC signal detector 116 and a power margin information detector 117.

The DRC signal detector 116 detects a DRC signal from the demodulatedsignal generated by the demodulator 115, and outputs the detected DRCsignal to the allocation section 101. The power margin informationdetector 117 detects power margin information from the demodulatedsignal generated by the demodulator 115, and outputs the detected powermargin information to a power setting section 118.

Using power margin information from the power margin informationdetector 117, the power setting section 118 sets a transmit signaltransmission power value for each communication terminal apparatus, andoutputs the set transmission power values to the power controller 109.

FIG. 3 is a block diagram showing the configuration of a communicationterminal apparatus according to Embodiment 1 of the present invention.

In FIG. 3, a requested modulation method determination section 201determines a transmission rate at which a communication terminalapparatus can receive at the desired quality, based on a CIR measured bya CIR measurement section 214 described later herein, and outputs thedetermined transmission rate to a margin calculator 202 and DRC signalcreation section 203.

Based on the determined transmission rate, the requested modulationmethod determination section 201 also indicates a spreading code bywhich a received signal is to be multiplied to an adaptive despreader210, indicates the received signal modulation method to an adaptivedemodulator 211, and indicates the received signal decoding method to anadaptive decoding section 212.

Using the CIR measured by the CIR measurement section 214 describedlater herein and the transmission rate determined by the requestedmodulation method determination section 201, the margin calculator 202calculates a power margin and outputs information relating to thecalculated power margin—that is, power margin information—to a combiner215.

The DRC signal creation section 203 creates a DRC signal indicating thetransmission rate calculated by the requested modulation methoddetermination section 201, and outputs this DRC signal to the combiner215.

The combiner 215 generates a combined signal by combining the DRC signalfrom the DRC signal creation section 203 and power margin informationfrom the margin calculator 202, and outputs the generated combinedsignal to a modulator 204.

The modulator 204 modulates the combined signal from the combiner 215and outputs the resulting signal to a spreader 205. The spreader 205spreads the combined signal modulated by the modulator 204, and outputsthe resulting signal to a transmitting RF section 206. The transmittingRF section 206 converts the frequency of the combined signal spread bythe spreader 205 to a radio frequency, and outputs this signal to aduplexer 207.

The duplexer 207 transmits the combined signal that has undergonefrequency conversion by the transmitting RF section 206 to a basestation apparatus via an antenna 208. The duplexer 207 also outputs asignal transmitted by a base station apparatus and received via theantenna 208 (received signal) to a receiving RF section 209.

The receiving RF section 209 converts the frequency of a received signalfrom the duplexer 207 to baseband, and outputs the received signalconverted to baseband to the adaptive despreader 210 and a despreader213.

In accordance with an instruction from the requested modulation methoddetermination section 201, the adaptive despreader 210 despreads thereceived signal from the receiving RF section 209, extracts componentsother than the pilot signal (components corresponding to data) in thereceived signal, and outputs the extracted components to the adaptivedemodulator 211. In accordance with an instruction from the requestedmodulation method determination section 201, the adaptive demodulator211 demodulates the components extracted by the adaptive despreader 210,and generates a demodulated signal. The adaptive decoding section 212obtains receive data by decoding the demodulated signal from theadaptive demodulator 211 in accordance with an instruction from therequested modulation method determination section 201.

Meanwhile the despreader 213 despreads the received signal from thereceiving RF section 209, extracts the pilot signal component in thereceived signal, and outputs the extracted pilot signal component to theCIR measurement section 214. Using the pilot signal component from thedespreader 213, the CIR measurement section 214 measures the CIR andoutputs the measured CIR to the requested modulation methoddetermination section 201 and margin calculator 202.

Next, operations performed between the base station apparatus shown inFIG. 2 and the communication terminal apparatus shown in FIG. 3 will bedescribed.

First, at the start of communication, in the base station a pilot signalis modulated by a modulator 106, spread by a spreader 107, and output tothe multiplexer 108. Only the despread pilot signal is output from themultiplexer 108 to the power controller 109. The pilot signal from themultiplexer 108 is amplified by the power controller 109 so as to attaina predetermined transmission power value. The amplified pilot signal isfrequency-converted to a radio frequency by the transmitting RF section110, and is transmitted to communication terminal apparatuses from theantenna 112 via the duplexer 111. This pilot signal is transmitted tothe communication terminal apparatuses via a control channel.

The pilot signal (control channel signal) transmitted by the basestation apparatus is received at the antenna 208 of the communicationterminal apparatus. The signal received by the antenna 208 (receivedsignal) is output to the receiving RF section 209 via the duplexer 207.The received signal from the duplexer 207 is frequency-converted tobaseband by the receiving RF section 209, and despread by the despreader213. By this means, the pilot signal in the received signal is extractedby the despreader 213. The extracted pilot signal is output to the CIRmeasurement section 214.

In the CIR measurement section 214, the CIR is measured based on thepilot signal output by the despreader 213. The measured CIR is sent tothe requested modulation method determination section 201 and margincalculator 202.

In the requested modulation method determination section 201, atransmission rate at which it is possible for this communicationterminal apparatus to receive at the desired quality is determined basedon the CIR measured by the CIR measurement section 214. The transmissionrate determination method used by the requested modulation methoddetermination section 201 will now be described using FIG. 4. FIG. 4 isa diagram showing the method of transmission rate determination by therequested modulation method determination section 201 of a communicationterminal apparatus according to Embodiment 1 of the present invention.

In the requested modulation method determination section 201, based onthe CIR (reception quality) measured by the CIR measurement section 214,a transmission rate to be requested of the base station is determined sothat the received signal characteristics (error rate characteristics) ofthis communication terminal apparatus meet the desired quality, and datatransmission efficiency is optimal.

Specifically, when, for example, the CIR measured by the CIR measurementsection 214 is a value as shown in FIG. 4 (reception CIR 301),transmission rates at which the received signal characteristics of thiscommunication terminal apparatus meet the desired quality (assuming aBit Error Rate (BER) of 10⁻³) are any of the following: the transmissionrate for QPSK, the transmission rate for 16QAM, and the transmissionrate for 64QAM. Of these transmission rates, the transmission rate atwhich data transmission efficiency is optimal is that for 64QAM. As aresult, when a CIR such as that shown in FIG. 4 is measured, thetransmission rate for 64QAM is determined as the transmission rate to berequested of the base station apparatus.

The transmission rate determined by the requested modulation methoddetermination section 201 as described above is output to the margincalculator 202 and DRC signal creation section 203. After thetransmission rate has been determined, a signal indicating the spreadingcode by which a received signal is to be multiplied, a signal indicatingthe received signal modulation method, and a signal indicating thereceived signal decoding method are output from the requested modulationmethod determination section 201 to the adaptive despreader 210,adaptive demodulator 211, and adaptive decoding section 212,respectively.

In the margin calculator 202, a power margin is calculated using the CIRmeasured by the CIR measurement section 214 and the transmission ratedetermined by the requested modulation method determination section 201.That is to say, in the margin calculator 202, the transmission ratedetermined by the requested modulation method determination section 201is first applied, and the difference between reception quality whentransmission is performed from the base station at the requestedtransmission rate (hereinafter referred to as “first reception quality”)and the minimum reception quality necessary for the received signalcharacteristics in this case to meet the desired quality (hereinafterreferred to as “second reception quality”) is calculated. A power marginis then calculated as a power value corresponding to the calculateddifference. This power margin is equivalent to the difference betweenthe transmission power value in the base station apparatus necessary inorder for this communication terminal apparatus to obtain the firstreception quality (normally transmitted transmission power) and thetransmission power value in the base station apparatus necessary forthis communication terminal apparatus to obtain the second receptionquality.

Specifically, with reference to FIG. 4, the minimum second receptionquality (CIR 302) necessary for the received signal characteristics tomeet the desired quality (BER=10⁻³) is first calculated in accordancewith a curve showing the CIR vs BER characteristic of the transmissionrate determined by the requested modulation method determination section201 (transmission rate for 64QAM). The difference between the firstreception quality (reception CIR 301) and second reception quality (CIR302) is then calculated, and then the power value corresponding to thecalculated difference is calculated as the power margin 303.

In order to calculate the power margin, it is also possible to firstcalculate the transmission power value in the base station apparatusnecessary for this communication terminal apparatus to obtain the firstreception quality, and the transmission power value in the base stationapparatus necessary for this communication terminal apparatus to obtainthe second reception quality, and then calculate the difference betweenthe transmission power values.

Information relating to a power margin calculated as described above isoutput to the combiner 215 as power margin information.

In the DRC signal creation section 203, a DRC signal indicating thetransmission rate calculated by the requested modulation methoddetermination section 201 is created. The created DRC signal is outputto the combiner 215.

In the combiner 215, a combined signal is generated by combining the DRCsignal from the DRC signal creation section 203 and power margininformation from the margin calculator 202. The generated signal isoutput to the modulator 204.

The combined signal is modulated by the modulator 204, spread by thespreader 205, frequency-converted to a radio frequency by thetransmitting RF section 206, and transmitted to the base stationapparatus by the antenna 208 via the duplexer 207.

The signal transmitted by the communication terminal apparatus isreceived by the antenna 112 of the base station apparatus. The signalreceived by the antenna 112 (received signal) is output to the receivingRF section 113 via the duplexer 111. The received signal from theduplexer 111 is frequency-converted to baseband by the receiving RFsection 113, despread by the despreader 114, and demodulated by thedemodulator 115. As a result, a demodulated signal is generated by thedemodulator 115. The generated demodulated signal is output to the DRCsignal detector 116 and power margin information detector 117.

In the power margin information detector 117, power margin informationis detected from the demodulated signal from the demodulator 115. Thedetected power margin information is output to the power setting section118.

In the power setting section 118, the power margin of each communicationterminal apparatus is recognized by means of the detected power margininformation. In the power setting section 118, also, a transmit signaltransmission power value is set for each communication terminalapparatus, taking account of the recognized power margin of thecommunication terminal apparatuses. Specifically, whereas inconventional adaptive modulation communication the transmit signaltransmission power of each communication terminal apparatus is alwaystaken as a predetermined transmission power value (constant), in thisembodiment a value obtained by subtracting the power margin of acommunication terminal apparatus from a predetermined transmission powervalue is set as the transmit signal transmission power value of thatcommunication terminal apparatus. A communication terminal apparatustransmit signal transmission power value set in this way is equivalentto the transmission power value of the base station apparatus necessaryfor that communication terminal apparatus to obtain the second receptionquality when the transmission rate requested by that communicationterminal apparatus is applied.

The transmit signal transmission power values of each communicationterminal apparatus set by the power setting section 118 in this way areoutput to the power controller 109.

Meanwhile, in the DRC signal detector 116, a DRC signal is detected fromthe demodulated signal generated by the demodulator 115. The detectedDRC signal is output to the allocation section 101.

In the allocation section 101, communication resource allocation to eachcommunication terminal apparatus is carried out based on the DRC signaltransmitted by each communication terminal apparatus. Downlink transmitdata sent from the base station apparatus to a communication terminalapparatus is stored in the buffer 102 until communication resourceallocation is carried out.

Downlink transmit data output from the buffer 102 is coded by theadaptive coding section 103 using a coding method enabling reception bya communication terminal apparatus, demodulated by the adaptivemodulator 104 using a demodulation method enabling reception by acommunication terminal apparatus, spread by the adaptive spreader 105using a spreading code enabling reception by a communication terminalapparatus, and output to the multiplexer 108. In the multiplexer 108, atransmit signal is generated by having a spread pilot signal in thespread downlink transmit data time-multiplexed.

The transmit signal generated by the multiplexer 108 is amplified in thepower controller 109 so as to attain the transmission power value set bythe power setting section 118. The amplified transmit signal isfrequency-converted to a radio frequency by the transmitting RF section110, and transmitted to communication terminal apparatuses by theantenna 112 via the duplexer 111.

The signal transmitted by the base station apparatus is received by theantenna 208 of the communication terminal apparatus. The signal receivedby the antenna 208 (received signal) is output to the receiving RFsection 209 via the duplexer 207. The received signal from the duplexer207 is frequency-converted to baseband by the receiving RF section 209,and despread by the adaptive despreader 210. By this means, componentsother than the pilot signal (components corresponding to data) in thereceived signal are extracted by the adaptive despreader 210. Theextracted non-pilot-signal components are demodulated by the adaptivedemodulator 211 and decoded by the adaptive decoding section 212. Bythis means, received data is obtained.

Next, the effects of a communication terminal apparatus according tothis embodiment will be described with reference to FIG. 5. FIG. 5 is adiagram showing how a communication terminal apparatus and base stationapparatus according to Embodiment 1 of the present invention performadaptive modulation communication.

In FIG. 5, the base station apparatus 401 corresponds to the basestation apparatus shown in FIG. 2, and communication terminalapparatuses 402 through 404 and communication terminal apparatuses 410through 412 correspond to the communication terminal apparatuses shownin FIG. 3. It is assumed that the base station apparatus 401 iscurrently performing communication with communication terminalapparatuses 402 through 404, which are within the cell area 405 coveredby this base station apparatus 401. It is also assumed thatcommunication terminals 410 through 412 are within the range of the cellarea 405, but are performing communication with a base station otherthan this base station 401. As cell areas are normally designed so as tooverlap, communication terminal apparatuses 410 through 412 are withinthe an area that overlaps the cell area of base station apparatus 401and the cell area of a base station other than base station apparatus401.

As described above, the base station apparatus 401 performs schedulingbased on the communication mode selected by communication terminalapparatuses 402 through 404, sets a transmission rate for eachcommunication terminal apparatus, and notifies a signal indicatingcommunication resource allocation to communication terminal apparatuses402 through 404 via a control channel. The base station apparatus 401then transmits data only to the relevant communication terminalapparatus in its assigned time via a data channel.

Here, as an example, the time will be considered in which the basestation apparatus 401 transmits data to communication terminal apparatus402. According to the conventional method, when the base stationapparatus 401 transmits data to a predetermined communication terminalapparatus, it uses transmission power high enough to ensure thatreception quality is sufficiently good at all communication terminalapparatuses in the cell area 405. In this case, as described above, acommunication terminal apparatus among communication terminalapparatuses 410 through 412 receiving data from another base stationapparatus will receive interference due to a signal transmitted tocommunication terminal apparatus 402 from base station apparatus 401.

However, in this embodiment, base station apparatus 401 does nottransmit data to communication terminal apparatus 402 using atransmission power value high enough to ensure that reception quality issufficiently good at all communication terminal apparatuses in the cellarea 405. That is to say, when base station apparatus 401 applies thetransmission rate requested by communication terminal apparatus 402, itstransmits data to communication terminal apparatus 402 using the minimumtransmission power value necessary to ensure that the received signalcharacteristics of communication terminal apparatus 402 meet the desiredquality. This minimum necessary transmission power value is equivalentto the minimum transmission power value necessary to ensure that thereception quality of a communication terminal apparatus within area 406meets the desired quality.

If base station apparatus 401 transmits data to communication terminalapparatus 402 using this kind of transmission power value, interferencereceived by communication terminal apparatuses 410 through 412 thatreceive data from another base station apparatus due to a signaltransmitted by base station apparatus 401 to communication terminalapparatus 402 will be suppressed. At this time, communication terminalapparatus 402 can obtain a received signal that meets the desiredquality.

Also, it goes without saying that base station apparatus 401 andcommunication terminal apparatuses 402 through 404 perform ordinary CDMAcommunication in parallel in a different band from that for adaptivemodulation communication.

In this embodiment, a case has been described where a base stationapparatus transmits data to only one communication terminal apparatus atone time, but the present invention can also be applied to a case wherea base station apparatus transmits data to a plurality of communicationterminal apparatuses at the same time. In this case, it is possible tosuppress mutual interference of delayed waves of signals transmittedfrom the base station apparatus to a plurality of communication terminalapparatuses, thereby enabling good communication quality to bemaintained for a plurality of communication terminal apparatuses.

Thus, in this embodiment, when adaptive modulation communication isperformed a base station apparatus does not transmit data to acommunication terminal apparatus using a transmission power value thatensures that reception quality is sufficiently good at all communicationterminal apparatuses within the cell covered by that base stationapparatus, but instead transmits data to a communication terminalapparatus using the minimum transmission power value necessary to ensurethat the received signal characteristics of that communication terminalapparatus meet the desired quality. By this means it is possible tomaintain the quality of a received signal in a communication terminalapparatus at the desired quality while suppressing interference withcommunication terminal apparatuses, among the communication terminalapparatuses within the area covered by that base station apparatus, thatperform adaptive modulation communication with another base stationapparatus.

Also, in this embodiment, a case has been described, as an example,where a communication terminal apparatus determines a transmission rateand power margin based on measured reception quality, and reports thedetermined transmission rate and power margin to a base stationapparatus, after which the base station apparatus sets a transmissionpower value of a transmit signal for that communication terminalapparatus using the reported transmission rate and power margin, but itis also possible for a communication terminal apparatus to report ameasured reception quality to a base station apparatus, and for the basestation apparatus to set a transmission power value of a transmit signalfor that communication terminal apparatus using a transmission rate andpower margin determined based on the reported reception quality. By thismeans it is possible to hold down the scale and power consumption of acommunication terminal apparatus.

Moreover, transmission of a power margin from a communication terminalapparatus may be performed only when DRC of the fastest data rate isrequested. By this means it is possible to hold down the scale and powerconsumption of a communication terminal apparatus. In this case, beingable to request a high transmission rate means that the CIR is good, andtherefore the probability of being located near a base station is high.Thus, base station transmission power can be greatly reduced, which ishighly effective in preventing interference.

Embodiment 2

In this embodiment, a case is described where reduction of transmissionpower is taken into consideration beforehand when DRC selection isperformed in a communication terminal apparatus. This embodiment isdescribed below.

First, the configuration of a communication terminal apparatus accordingto this embodiment will be described with reference to FIG. 6. FIG. 6 isa block diagram showing the configuration of a communication terminalapparatus according to Embodiment 2 of the present invention. Parts inFIG. 6 identical to those in Embodiment 1 (FIG. 3) are assigned the samecodes as in FIG. 3 and their detailed explanations are omitted.

In FIG. 6, a DRC signal creation section 501 creates a DRC signal usinga transmission rate determined by a requested modulation methoddetermination section 201 and power margin information output from amargin calculator 202. The DRC signal creation section 501 also outputsthe created DRC signal to a modulator 502. A detailed description of theDRC signal in this embodiment will be given later herein.

The modulator 502 modulates the DRC signal from the DRC signal creationsection 501 and outputs the resulting signal to a spreader 205.

Next, the configuration of a base station apparatus according to thisembodiment will be described with reference to FIG. 7. FIG. 7 is a blockdiagram showing the configuration of a base station apparatus accordingto Embodiment 2 of the present invention. Parts in FIG. 7 identical tothose in Embodiment 1 (FIG. 2) are assigned the same codes as in FIG. 2and their detailed explanations are omitted.

In FIG. 7, a power setting section 601 sets a transmit signaltransmission power value for each communication terminal apparatus usingthe DRC signal detected by a DRC signal detector 116, and outputs theset transmission power values to a power controller 602.

Power controller 602 amplifies transmit data spread by an adaptivespreader 105 so as to attain the transmission power value set by thepower setting section 601, and outputs the amplified transmit data to amultiplexer 604.

A power controller 603 amplifies a pilot signal spread by a spreader 107so as to attain a predetermined (constant) transmission power value, andoutputs the amplified pilot signal to the multiplexer 604.

The multiplexer 604 generates a multiplex signal by multiplexing thetransmit data amplified by power controller 602 with the pilot signalamplified by power controller 603, and outputs the generated multiplexsignal to a transmitting RF section 110.

Next, operations performed between the communication terminal apparatusshown in FIG. 6 and the base station apparatus shown in FIG. 7 will bedescribed. Descriptions of operations in this embodiment that areidentical to those in Embodiment 1 are omitted, and only operations inthis embodiment that differ from those in Embodiment 1 are described.

In FIG. 6, a transmission rate at which a communication terminalapparatus can receive at the desired quality is determined by therequested modulation method determination section 201 based on a CIRmeasured by the CIR measurement section 214, as described inEmbodiment 1. The transmission rate determined by the requestedmodulation method determination section 201 is output to the margincalculator 202 and DRC signal creation section 501.

In the margin calculator 202, a power margin is calculated using the CIRmeasured by the CIR measurement section 214 and the transmission ratedetermined by the requested modulation method determination section 201,as described in Embodiment 1. Information relating to the calculatedpower margin is output to the DRC signal creation section 501 as powermargin information.

In the DRC signal creation section 501, a DRC signal is created usingthe transmission rate determined by the requested modulation methoddetermination section 201 and power margin information from the margincalculator 202. Specifically, a DRC table showing DRC signalscorresponding to transmission rates and power margin information isprovided beforehand in the DRC signal creation section 501, and a DRCsignal is determined unconditionally based on the transmission rate fromthe requested modulation method determination section 201 and powermargin information from the margin calculator 202.

Whereas a DRC signal in Embodiment 1 “indicates a transmission rate atwhich reception is possible by a communication terminal apparatus at thedesired quality”, in this embodiment a DRC signal indicates “(1) atransmission rate at which reception is possible by a communicationterminal apparatus at the desired quality and (2) the power margin whenthis transmission rate is selected (this power margin being of the samekind as that in Embodiment 1)”.

An actual example of a DRC table used by the DRC signal creation section501 will now be described with reference to FIG. 8. FIG. 8 is a diagramshowing an example of a DRC table used by a communication terminalapparatus according to Embodiment 2 of the present invention.

In the DRC table shown in FIG. 8, DRC signals (1 through 6) are givencorrespondence to the modulation method (BPSK, QPSK, 16QAM, etc.)corresponding to the transmission rate determined by the requestedmodulation method determination section 201 and power margin information(0, 5, 10, 15 [dB], etc.) from the margin calculator 202.

For example, when a transmission rate for 16QAM is selected by therequested modulation method determination section 201 and a power marginof 5 [dB] is calculated by the margin calculator 202 (i.e. the desiredquality can be met even if transmission power is decreased by 5 [dB]), aDRC signal with signal content of “4” is determined.

A DRC signal created by the DRC signal creation section 501 in this wayis modulated by the modulator 502 and then output to the spreader 205.

In FIG. 7, a DRC signal detected by the DRC signal detector 116 isoutput to the allocation section 101 and power setting section 601. Inthe allocation section 101, the kind of processing described inEmbodiment 1 is executed.

In the power setting section 601, a transmit signal transmission powervalue for each communication terminal apparatus is set based on the DRCsignal from the DRC signal detector 116. Specifically, in the powersetting section 601, the power margin corresponding to the DRC signalfrom the DRC signal detector 116 is recognized using the DRC table usedby the communication terminal apparatus shown in FIG. 6. Also, the valueobtained by subtracting this power margin from a predeterminedtransmission power value is set as the transmit signal transmissionpower value for this communication terminal apparatus.

For example, when the DRC signal of a particular communication terminalapparatus is “4”, in the power setting section 601 it is recognized thata request to lower the transmission power value by 5 [dB] has been madeby this communication terminal apparatus, and the transmission powervalue of this communication terminal apparatus is set as the valueobtained by subtracting 5 [dB] from the predetermined transmission powervalue. The transmission power value set in this way is output to powercontroller 602.

In power controller 602, transmit data spread by the adaptive spreader105 is amplified so as to attain the transmission power value set by thepower setting section 601. The amplified transmit data is then output tothe multiplexer 604.

In power controller 603, a pilot signal spread by the spreader 107 isamplified so as to always attain a predetermined (virtually constant)transmission power value. The amplified pilot signal is then output tothe multiplexer 604.

The transmit data amplified by power controller 602 and pilot signalamplified by power controller 603 are multiplexed by the multiplexer604. By this means a multiplex signal is generated. The generatedmultiplex signal is output to the transmitting RF section 110. Thiscompletes the operations performed between the communication terminalapparatus shown in FIG. 6 and the base station apparatus shown in FIG.7.

As described above, in this embodiment a communication terminalapparatus does not transmit information indicating a transmission rate(modulation method) and information indicating a power marginindividually to abase station apparatus (as in Embodiment 1), butinstead a communication terminal apparatus transmits to a base stationapparatus information indicating a combination of transmission rate(modulation method) and power margin. By this means it is possible toreduce the amount of information (transmission rate and transmissionpower value related information) transmitted by a communication terminalapparatus to a base station apparatus—that is to say, the amount ofinformation in a radio channel.

For example, to consider the amount of information necessary for powermargin transmission, in Embodiment 1, if the power margin handled is a2-digit value (0 to 99 [dB]) at least 7 bits of information arenecessary for the power margin alone, whereas in Embodiment 2, 16 kindsof information indicating a combination of transmission rate and powermargin can be transmitted with only 4 bits of information.

Also, in this embodiment, having a base station apparatus alwaystransmit a pilot signal (signal used as a reference when communicationquality is measured in a communication terminal apparatus: referencesignal) with a virtually constant transmission power value enables acommunication terminal apparatus to measure communication qualityaccurately, thereby enabling DRC selection (modulation method and powermargin selection) to be performed accurately.

Furthermore, if transmission of a pilot signal by a base stationapparatus with an always virtually constant transmission power value isapplied to Embodiment 1, the same kind of effect is obtained as inEmbodiment 2.

In this embodiment of the present invention, a case has been describedwhere a DRC table is used in which combinations of modulation method andpower margin are set beforehand, but the contents of this DRC table(such as power reductions of 5 [dB] and 10 [dB] in the case of 16QAMtransmission, for example) may also be reported in advance from a basestation apparatus to a communication terminal apparatus by means of abroadcast channel before communication is carried out.

It is also possible to select the optimal power reduction by adaptivelychanging the DRC table contents for each communication terminalapparatus according to various conditions, such as communicationquality, even during communication.

Moreover, in this embodiment, a case has been described where a DRCsignal indicating a combination of transmission rate and power margin istransmitted, but it is also possible for a communication terminalapparatus to calculate a transmission power value in a base stationapparatus based on a power margin, and transmit a DRC signal indicatinga combination of transmission rate and this calculated transmissionpower value, and for the base station apparatus to set a transmissionpower value using the transmission power value in this DRC signal.

Embodiment 3

In this embodiment, a case is described where, when transmit datacommunications to communication terminal apparatuses with goodcommunication quality become predominant in base station apparatusdownlinks (data channels), the transmission power of the pilot signaland transmit data to all communication terminal apparatuses is reduced.

When transmit data communications to communication terminal apparatuseswith good communication quality—that is, communication terminalapparatuses at locations near a base station apparatus (for example,communication terminal apparatuses reporting a DRC signal of 4 to 6 inFIG. 8)—are predominant in downlinks within the base station apparatuscell, it is probable that there will be few cases where a downlink isallocated to a communication terminal apparatus at the edge of this cell(a communication terminal apparatus at a location far from the basestation apparatus). With the conventional method, even in a case such asthis the base station apparatus transmits a pilot signal and transmitdata using constant power capable of reaching all communication terminalapparatuses within the cell.

However, to consider firstly transmit data, in the above kind of case abase station apparatus transmits transmit data to a communicationterminal apparatus at a location near that base station apparatus usingconstant power that ensures good reception quality at a communicationterminal apparatus at a location far from that base station apparatus,even though there is little possibility of transmitting transmit data tothat communication terminal apparatus at a location far from that basestation apparatus. That is to say, the base station apparatus uses morethan the necessary transmission power in transmitting transmit data to acommunication terminal apparatus.

As a result, the base station apparatus imposes major interference oncommunication terminal apparatuses in a cell covered by another basestation apparatus. Also, when the base station apparatus performsadaptive modulation communication with a plurality of communicationterminal apparatuses at the same time, it imposes major interference onthe plurality of communication terminal apparatuses in the cell coveredby itself.

Secondly, to consider a pilot signal, in the above kind of case a basestation apparatus transmits a pilot signal using power capable ofreaching all communication terminal apparatuses within the cell. Here,there is little possibility of the base station apparatus transmittingtransmit data to a communication terminal apparatus at a location farfrom that base station apparatus. Thus, to consider only the situationwhere transmit data communications to communication terminal apparatuseswith good communication quality have become predominant in base stationapparatus downlinks, there is little need for a base station apparatusto transmit a pilot signal to a communication terminal apparatus at alocation far from that base station apparatus. Therefore, a base stationapparatus can be said to use more than the necessary transmission powerin transmitting a pilot signal.

Moreover, the use of more than the necessary transmission power by abase station apparatus in transmitting a pilot signal is equivalent toimposing interference on communication terminal apparatuses in the cellof another base station apparatus.

Thus, in this embodiment, in order to prevent the above-describedproblem, when transmit data communications to communication terminalapparatuses with good communication quality have become predominant inbase station apparatus downlinks (that is, when downlink quality isexcessive), the base station apparatus not only reduces the transmissionpower of transmit data for communication terminal apparatuses with goodcommunication quality, but also reduces the transmit data transmissionpower and pilot signal transmission power for other communicationterminal apparatuses to the same level as the transmit data transmissionpower for communication terminal apparatuses with good communicationquality.

That is to say, a base station apparatus reduces its cell radius (aseach communication terminal apparatus measures communication qualityusing the CIR of a pilot signal, reduction of the pilot signaltransmission power by a base station apparatus is equivalent to havingthe base station apparatus reduce the size of its cell). In other words,a base station apparatus transmits transmit data in a concentratedfashion, using less power than the normal transmission power, tocommunication terminal apparatuses at locations near that base stationapparatus from among communication terminal apparatuses selected astransmit data transmission destinations, and as regards communicationterminal apparatuses at locations far from that base station apparatus,either has them accommodated in the cell of another base stationapparatus, or performs transmit data transmission after transmit datatransmission to communication terminal apparatuses at locations near thebase station apparatus is completed.

By this means, a base station apparatus can suppress interference toother cells while performing communication of transmit data tocommunication terminal apparatuses with good communication quality in aconcentrated fashion.

When transmit data communications to communication terminal apparatuseswith good communication quality become few in number, the base stationapparatus restores the transmit data transmission power and pilot signaltransmission power to their original levels (restores the cell to itsoriginal size) and ensures that transmit data and the pilot signal reachall communication terminal apparatuses within the cell at sufficientquality. That is to say, at this time the base station apparatus notesthat many of the communication terminal apparatuses selected as transmitdata transmission destinations are communication terminal apparatuses atlocations far from that base station apparatus, and restores thetransmit data transmission power and pilot signal transmission power totheir original levels.

By having all base station apparatuses perform transmission powercontrol as described above, it is possible to reduce interference powerbetween base station apparatuses. As a result, all base stationapparatuses can reduce power consumption, enabling radio resources to beused more effectively.

Next, the configuration of the above base station apparatus will bedescribed with reference to FIG. 9. FIG. 9 is a block diagram showingthe configuration of a base station apparatus according to Embodiment 3of the present invention. Here, as an example, a case is described wherethe base station apparatus shown in FIG. 9 performs communication withthe communication terminal apparatus shown in FIG. 6 using the DRC tableshown in FIG. 8, but a communication terminal apparatus that performscommunication with the base station apparatus shown in FIG. 9 may be ofany kind as long as it has a configuration whereby a DRC signal isnotified to the base station apparatus. Parts in FIG. 9 identical tothose in FIG. 2 or FIG. 7 are assigned the same codes as in FIG. 2 orFIG. 7 and their detailed explanations are omitted.

As in Embodiment 1, an allocation section 101 determines communicationresource allocation to each communication terminal apparatus based on aDRC signal (transmit data transmission is allocated preferentially tocommunication terminal apparatuses notifying a high DRC signal).

Using a DRC signal from a DRC signal detector 116, a downlink qualityestimation section 801 recognizes how many communication terminalapparatuses are communication terminal apparatuses at locations nearthis base station apparatus—that is, communication terminal apparatuseswith good communication quality (communication terminal apparatuseswhose pilot signal CIR is greater than a predetermined value), and basedon the result of this recognition, generates information indicatingtransmission power and outputs this to a power setting section 802.

The power setting section 802 sets a pilot signal and transmit datatransmission power value based on information from the downlink qualityestimation section 801, and outputs the set transmission power value toa power controller 109.

Next, the operation of a base station apparatus with the aboveconfiguration will be described with reference to FIG. 9 and FIG. 10.FIG. 10 is a flowchart showing the operation of a base station apparatusaccording to Embodiment 3 of the present invention. Operations in thisembodiment identical to operations in Embodiment 1 or Embodiment 2 areomitted.

In the downlink quality estimation section 801, first, as shown in step(hereinafter referred to as “ST”) 901, when the number of communicationterminal apparatuses reporting a DRC value of 6, or the proportion ofcommunication terminal apparatuses reporting a DRC value of 6 among allcommunication terminal apparatuses that perform communication within thecell of this base station apparatus (hereinafter referred to as simply“the number or proportion of DRC-value-6 communication terminalapparatuses”) exceeds a predetermined value, information indicating thatthe transmission power value is to be reduced by 15 [dB] below normal isoutput to the power setting section 802 as shown in ST902. When, on theother hand, the number or proportion of DRC-value-6 communicationterminal apparatuses does not exceed the predetermined value, theprocessing flow proceeds to ST903.

In ST903, when the number or proportion of DRC-value-5-pluscommunication terminal apparatuses exceeds a predetermined value,information indicating that the transmission power value is to bereduced by 10 [dB] below normal is output to the power setting section802 as shown in ST904. When, on the other hand, the number or proportionof DRC-value-5-plus communication terminal apparatuses does not exceedthe predetermined value, the processing flow proceeds to ST905.

In ST905, when the number or proportion of DRC-value-4-pluscommunication terminal apparatuses exceeds a predetermined value,information indicating that the transmission power value is to bereduced by 5 [dB] below normal is output to the power setting section802 as shown in ST906. When, on the other hand, the number or proportionof DRC-value-4-plus communication terminal apparatuses does not exceedthe predetermined value, the processing flow proceeds to ST907.

In ST907, it is recognized that transmit data communications tocommunication terminal apparatuses with good communication quality arenot predominant in base station apparatus downlinks, and informationindicating that the transmission power value is to be restored to normalis output to the power setting section 802.

Thereafter, in the power setting section 802 the pilot signal andtransmit data transmission power value is set based on informationindicated by the downlink quality estimation section 801. That is tosay, based on information from the downlink quality estimation section801, the pilot signal and transmit data transmission power value is setby subtracting one or other of 15 [dB] (ST902), 10 [dB] (ST904), 5 [dB](ST906), or 0 [dB] (ST907) from the normal transmission power value. Itgoes without saying that “normal transmission power value” here isequivalent to a transmission power value that enables all communicationterminal apparatuses in the cell of this base station apparatus toreceive at sufficient quality.

Setting a value to be subtracted from the normal transmission powervalue according to the size of the DRC value (ST902, St904, ST906, andST907 in FIG. 10) is done in consideration of the fact that the optimalvalue of a transmission power value for a communication terminalapparatus differs according to the size of the DRC value reported bythat communication terminal apparatus—that is, the distance of thatcommunication terminal apparatus from the base station apparatus. Bythis means it is possible to reliably maintain good reception quality incommunication terminal apparatuses that receive transmit data.

Thereafter, a transmit signal generated by a multiplexer 108 (a signalin which a pilot signal and transmit data for each communicationterminal apparatus is multiplexed) is uniformly amplified by the powercontroller 109 so as to attain the transmission power value set by thepower setting section 802, and is output to the transmitting RF section110.

Next, the reason for reducing not only the transmission power value oftransmit data for all communication terminal apparatuses but also thepilot signal transmission power value will be explained. If only thetransmit data transmission power value were reduced and the pilot signaltransmission power value were made the normal value, there would be apossibility of reception quality when receiving a pilot signal incommunication terminal apparatuses in the cell of another base stationapparatus being lower than reception quality when actually receivingtransmit data. Thus, these communication terminal apparatuses wouldreport to the base station apparatus a lower transmission rate than theactual transmission rate sufficient to meet the predetermined receptionquality. As a result, the downlink total throughput (total transmit datatransmitted to communication terminal apparatuses) in theabove-mentioned other base station apparatus would fall.

Thus, in this embodiment, the transmit data and pilot signaltransmission power values for all communication terminal apparatuses arereduced to the same level. By this means it is possible to prevent afall in total throughput in another base station apparatus.

Thus, according to this embodiment, by having a base station apparatusdetermine the transmission power value of the pilot signal and transmitdata for all communication terminal apparatuses according to theproportion of transmit data communications on downlinks to communicationterminal apparatuses with good communication quality (located near thebase station apparatus)—that is, the proportion of transmit datacommunications to communication terminal apparatuses with goodcommunication quality on downlinks—it is possible to suppressinterference to communication terminal apparatuses present in the cellof that base station apparatus and the cell of another base stationapparatus, and also to improve downlink total throughput (the totalamount of transmit data transmitted to communication terminalapparatuses).

Specifically, when the proportion of transmit data communications tocommunication terminal apparatuses with good communication quality ondownlinks is large, by uniformly reducing the transmission power valuesof the pilot signal and transmit data for all communication terminalapparatuses it is possible to maintain reception quality in thosecommunication terminal apparatuses with good communication quality whilesuppressing interference to communication terminal apparatuses presentin the cell of the relevant base station apparatus and the cell ofanother base station apparatus.

When, on the other hand, the proportion of transmit data communicationsto communication terminal apparatuses with good communication quality ondownlinks is small, since reception quality in many communicationterminal apparatuses at locations far from the base station apparatuswill degrade, and consequently downlink total throughput will fall, whenthe transmission power values of the pilot signal and transmit data forall communication terminal apparatuses are kept reduced, thetransmission power values of the pilot signal and transmit data for allcommunication terminal apparatuses are made the normal values. By thismeans it is possible to increase downlink total throughput—that is, toimprove transmission efficiency.

Embodiment 4

In above-described Embodiment 3, pilot signal and transmit datatransmission power values are reduced according to the proportion oftransmit data communications to communication terminal apparatuses withgood communication quality on downlinks. However, reducing the transmitdata transmission power value may lead to the generation of a largenumber of packets that are not received correctly by communicationterminal apparatuses, and a fall in downlink total throughput, resultingin inefficient transmission.

Thus, in this embodiment, monitoring is carried out as to whether or notdownlink total throughput can be maintained, and if downlink totalthroughput falls after the transmit data transmission power value isreduced, the transmit data transmission power value is made to approachthe normal value.

The configuration of a base station apparatus according to thisembodiment will be described below with reference to FIG. 11. FIG. 11 isa block diagram showing the configuration of a base station apparatusaccording to Embodiment 4 of the present invention. Parts in FIG. 11identical to those in Embodiment 3 (FIG. 9) are assigned the same codesas in FIG. 9 and their detailed explanations are omitted.

Allocation section 1001 in FIG. 11 has the same configuration asallocation section 101 in Embodiment 3, except for the following point.Namely, allocation section 1001 outputs the results of communicationresource allocation to each communication terminal apparatus determinedon the basis of a DRC signal (which transmission rate is to be used fortransmission to which communication terminal apparatus) to a downlinkquality estimation section 1002.

Downlink quality estimation section 1002 has the same configuration asdownlink quality estimation section 801 in Embodiment 3, except for thefollowing point. Namely, downlink quality estimation section 1002monitors changes in overall downlink total throughput using allocationresults from the allocation section 1001, generates informationindicating transmission power based on the recognition results describedin Embodiment 3 and these changes in total throughput, and outputs thisinformation to a power setting section 802.

Next, the operation of a base station apparatus with the aboveconfiguration will be described with reference to FIG. 11 and FIG. 12.FIG. 12 is a flowchart showing the operation of a base station apparatusaccording to Embodiment 4 of the present invention. Detailedexplanations of operations in FIG. 12 identical to operations in FIG. 10are omitted.

After the transmission power value has been reduced by 15 [dB] belownormal in ST902, as shown in ST1101 the downlink quality estimationsection 1002 monitors downlink total throughput based on allocationresults from the allocation section 1001, and determines whether or nottotal throughput has fallen compared to prior to the reduction intransmission power. When total throughput is not fallen, the processingflow proceeds to above-described ST901. When total throughput is fallen,the processing flow proceeds to above-described ST904.

Similarly, after the transmission power value has been reduced by 10[dB] below normal in ST904, as shown in ST1102 the downlink qualityestimation section 1002 determines whether or not total throughput hasfallen compared to prior to the reduction in transmission power. Whentotal throughput is not fallen, the processing flow proceeds toabove-described ST901. When total throughput is fallen, the processingflow proceeds to above-described ST906.

Similarly, again, after the transmission power value has been reduced by5 [dB] below normal in ST906, as shown in ST1103 the downlink qualityestimation section 1002 determines whether or not total throughput hasfallen compared to prior to the reduction in transmission power. Whentotal throughput is not fallen, the processing flow proceeds toabove-described ST901. When total throughput is fallen, the processingflow proceeds to above-described ST907.

In this embodiment, a case has been described where, when totalthroughput after a reduction in the transmission power value cannot bemaintained at the total throughput prior to the reduction in thetransmission power value, the transmission power value is gradually madeto approach the normal value (the transmission power value is graduallyraised), but the transmission power value may also be restored directlyto its normal value.

Thus, according to this embodiment, a fall in downlink total throughputcaused by reducing the transmission power value can be prevented bycausing the pilot signal and transmit data transmission power value toapproach the normal value in accordance with changes in downlink totalthroughput. By this means it is possible to achieve efficient transmitdata transmission.

Embodiment 5

In this embodiment, a case is described where a base station apparatusdetects, based on the number of communication terminal apparatusesnotifying a predetermined DRC signal, whether or not transmit datacommunications to communication terminal apparatuses with goodcommunication quality (communication terminal apparatuses at locationsnear that base station apparatus) have become predominant in basestation apparatus downlinks (that is, whether or not downlink quality isexcessive), and furthermore changes the transmission power of the pilotsignal and transmit data for all communication terminal apparatusesbased on the result of detection.

In above-described Embodiment 3, detection is performed as to whether ornot transmit data communications to communication terminal apparatuseswith good communication quality have become predominant on downlinkswithin a base station apparatus cell, using the number of communicationterminal apparatuses sending a predetermined DRC signal as a proportionof the total number of communication terminal apparatuses that aretransmit data transmission destinations.

However, in a case where, for example, the total number of communicationterminal apparatuses that are transmit data transmission destinations issmall, there is a possibility of total throughput falling when thetransmission power of the pilot signal and transmit data for allcommunication terminal apparatuses is reduced as a result of the aboveproportion exceeding a threshold value.

Thus, in this embodiment, detection is performed as to whether or nottransmit data communications to communication terminal apparatuses withgood communication quality have become predominant on downlinks, basedon the number of communication terminal apparatuses notifying apredetermined DRC signal, and the transmission power of the pilot signaland transmit data for all communication terminal apparatuses is changedbased on the result of this detection.

Specifically, when, for example, the number of communication terminalapparatuses notifying a predetermined DRC signal is greater than orequal to a threshold value, it is recognized that communications tocommunication terminal apparatuses with good communication quality havebecome predominant in downlinks, and in order to prevent transmissionfrom being performed using more than the necessary transmission power,the transmission power is reduced. When, on the other hand, the numberof communication terminal apparatuses notifying a predetermined DRCsignal is less than the threshold value, it is recognized that many ofthe communication terminal apparatuses that are transmit datatransmission destinations are at locations far from that base stationapparatus, and transmission power is restored to the normal power value.

By this means it is possible to suppress interference to communicationterminal apparatuses present in the cell of the relevant base stationapparatus and the cell of another base station apparatus, and also toimprove downlink total throughput.

Next, the configurations of a communication terminal apparatus and basestation apparatus according to this embodiment will be described withreference to FIG. 13 through FIG. 15. FIG. 13 is a block diagram showingthe configuration of a communication terminal apparatus according toEmbodiment 5 of the present invention, FIG. 14 is a diagram showing anexample of a DRC signal used by a communication terminal apparatusaccording to Embodiment 5 of the present invention, and FIG. 15 is ablock diagram showing the configuration of a base station apparatusaccording to Embodiment 5 of the present invention.

First, the configuration of a communication terminal apparatus will bedescribed with reference to FIG. 13. Parts in FIG. 13 identical to thosein FIG. 6 are assigned the same codes as in FIG. 6 and their detailedexplanations are omitted.

A DRC signal creation section 1201 creates a DRC signal using atransmission rate determined by a requested modulation methoddetermination section 201. Specifically, the DRC signal creation section1201 has a DRC table (such as the DRC table shown in FIG. 14, forexample) that shows DRC signals corresponding to transmission rates, andcreates the DRC signal corresponding to the transmission rate determinedby the requested modulation method determination section 201. This DRCsignal creation section 1201 outputs the created DRC signal to amodulator 502.

Next, the configuration of a base station apparatus will be describedwith reference to FIG. 15. Parts in FIG. 15 identical to those in FIG. 9are assigned the same codes as in FIG. 9 and their detailed explanationsare omitted.

Using a DRC signal from a DRC signal detector 116, a downlink qualityestimation section 1401 recognizes the number of communication terminalapparatuses at locations near this base station apparatus—that is,communication terminal apparatuses with good communication quality(communication terminal apparatuses whose pilot signal CIR is greaterthan a predetermined value), and compares the recognized number with athreshold value. This downlink quality estimation section 1401 generatesinformation indicating transmission power based on the result of thiscomparison, and outputs this information to a power setting section 802.

Next, the operation of a communication terminal apparatus and basestation apparatus with the above configurations will be described withreference to FIG. 16. FIG. 16 is a flowchart showing the operation of abase station apparatus according to Embodiment 5 of the presentinvention. Operations in this embodiment identical to operations inEmbodiment 1 through Embodiment 4 are omitted.

In the communication terminal apparatus shown in FIG. 13, a DRC signalcorresponding to the transmission rate determined by the requestedmodulation method determination section 201 is generated in the DRCsignal creation section 1201 in accordance with the DRC table shown inFIG. 14. The generated DRC signal is output to the modulator 502.

Operations in the base station apparatus shown in FIG. 15 are asfollows. First, as shown in ST1501, in the downlink quality estimationsection 1401 the number of communication terminal apparatuses reportinga DRC value of 3 is recognized using the DRC signal from detector 116,and then the recognized number is compared with a threshold value.

When the result of this comparison is that the number of communicationterminal apparatuses reporting a DRC value of 3 is greater than or equalto the threshold value, it is recognized that transmit datacommunications to communication terminal apparatuses with goodcommunication quality (communication terminal apparatuses reporting aDRC value of 3) have become predominant in downlinks, and, as shown inST1502, information indicating that transmission power is to be reducedby, for example, 1 [dB] is generated. When, on the other hand, thenumber of communication terminal apparatuses reporting a DRC value of 3is less than the threshold value, it is recognized that many of thecommunication terminal apparatuses that are transmit data transmissiondestinations are at locations far from this base station apparatus, andthe processing flow proceeds to ST1503.

In ST1503, it is determined whether or not the transmission power valueat the current point in time is the normal transmission power value(maximum value). When the transmission power value at the current pointin time is smaller than the normal transmission power value, informationindicating that transmission power is to be raised by, for example, 1[dB] is generated, as shown in ST1504. When, on the other hand, thetransmission power value at the current point in time is the normaltransmission power value, information indicating that transmission poweris not to be changed is generated, and the processing flow proceeds toST1501.

Information generated by the downlink quality estimation section 1401 asdescribed above is output to the power setting section 802. In the powersetting section 802, pilot signal and transmit data transmission powervalues are set based on the information indicated by the downlinkquality estimation section 1401.

Thus, in this embodiment, a base station apparatus determines thetransmission power value of the pilot signal and transmit data for allcommunication terminal apparatuses according to the number ofcommunication terminal apparatuses with good communication quality(communication terminal apparatuses at locations near the base stationapparatus), thereby making it possible to suppress interference tocommunication terminal apparatuses in the cell of that base stationapparatus and the cell of another base station apparatus, and also toimprove downlink total throughput.

Specifically, by uniformly reducing the transmission power value of thepilot signal and transmit data for all communication terminalapparatuses when the number of communication terminal apparatuses withgood communication quality is greater than or equal to a thresholdvalue, it is possible to maintain good reception quality in theabove-mentioned communication terminal apparatuses with goodcommunication quality while suppressing interference to communicationterminal apparatuses in the cell of that base station apparatus and thecell of another base station apparatus.

When, on the other hand, the number of communication terminalapparatuses with good communication quality on downlinks is less thanthe threshold value, since reception quality in many communicationterminal apparatuses at locations far from the base station apparatuswill degrade, and consequently downlink total throughput will fall, ifthe transmission power values of the pilot signal and transmit data forall communication terminal apparatuses are kept reduced, thetransmission power values of the pilot signal and transmit data for allcommunication terminal apparatuses are made to approach the normaltransmission power value. By this means it is possible to increasedownlink total throughput—that is, to improve transmission efficiency.

Moreover, according to this embodiment, when the total number ofcommunication terminal apparatuses that are transmit data transmissiondestinations is small, transmission power is changed on the basis of thenumber of communication terminal apparatuses with good communicationquality, thereby enabling a fall in downlink total throughput to besuppressed to a greater extent that in Embodiment 3.

In this embodiment, a case has been described, as an example, where acommunication terminal apparatus notifies to a base station apparatus aDRC signal specifying only the modulation method, but it goes withoutsaying that the present invention can also be applied to a case where acommunication terminal apparatus notifies a DRC signal of the kinddescribed in Embodiment 1 through Embodiment 4.

Also, in this embodiment, a case has been described where transmissionpower is changed on the basis of the number of communication terminalapparatuses with good communication quality in order to prevent a fallin downlink total throughput due to the fact that the total number ofcommunication terminal apparatuses that are transmit data transmissiondestinations is small, but, as in Embodiment 3 it goes without sayingthat it is also possible to change transmission power based on thenumber of communication terminal apparatuses with good communicationquality as a proportion of the total number of communication terminalapparatuses that are transmit data transmission destinations.

Embodiment 6

In above-described Embodiment 5, pilot signal and transmit datatransmission power values are reduced according to the number ofcommunication terminal apparatuses with good communication quality ondownlinks. However, as stated in Embodiment 4, reducing the transmitdata transmission power value may lead to the generation of a largenumber of packets that are not received correctly by communicationterminal apparatuses, and a fall in downlink total throughput, resultingin inefficient transmission.

Thus, in this embodiment, as in Embodiment 4, monitoring is carried outas to whether or not downlink total throughput can be maintained, andwhen downlink total throughput falls after the transmit datatransmission power value is reduced, the transmit data transmissionpower value is made to approach the normal value.

The configuration of a base station apparatus according to thisembodiment will be described below with reference to FIG. 17. FIG. 17 isa block diagram showing the configuration of a base station apparatusaccording to Embodiment 6 of the present invention. Parts in FIG. 17identical to those in FIG. 11 and FIG. 15 are assigned the same codes asin FIG. 11 and FIG. 15 and their detailed explanations are omitted.

Downlink quality estimation section 1601 in FIG. 17 has the sameconfiguration as downlink quality estimation section 1401 in Embodiment5, except for the following point. Namely, downlink quality estimationsection 1601 monitors changes in overall downlink total throughput usingallocation results from an allocation section 1001, generatesinformation indicating transmission power based on the comparisonresults described in Embodiment 5 and these changes in total throughput,and outputs this information to a power setting section 802.

The configuration of a communication terminal apparatus according tothis embodiment is the same as that in Embodiment 5 (FIG. 13), and adetailed explanation thereof is omitted here.

Next, the operation of a base station apparatus with the aboveconfiguration will be further described with reference to FIG. 18. FIG.18 is a flowchart showing the operation of a base station apparatusaccording to Embodiment 6 of the present invention. Detailedexplanations of operations in FIG. 18 identical to operations in FIG. 16are omitted.

After the transmission power value has been reduced by 1 [dB] in ST1502,as shown in ST1701 the downlink quality estimation section 1601 monitorsdownlink total throughput based on allocation results from theallocation section 1001, and determines whether or not total throughputhas fallen compared to prior to the reduction in transmission power.When total throughput has not fallen, the processing flow proceeds toabove-described ST1501. When total throughput has fallen, the processingflow proceeds to above-described ST1504.

In this embodiment, a case has been described where, when totalthroughput after a reduction in the transmission power value cannot bemaintained at the total throughput prior to the reduction in thetransmission power value, the transmission power value is gradually madeto approach the normal value (the transmission power value is graduallyraised), but the transmission power value may also be restored directlyto its normal value.

Thus, according to this embodiment, a fall in downlink total throughputcaused by reducing the transmission power value can be prevented bycausing the pilot signal and transmit data transmission power value toapproach the normal value in accordance with changes in downlink totalthroughput. By this means it is possible to achieve efficient transmitdata transmission.

Embodiment 7

In this embodiment, a case is described where the distribution of DRCvalues reported by communication terminal apparatuses is used, as wellas using just the number or proportion of communication terminalapparatuses reporting the highest DRC value, as an indicator fordetecting whether or not downlink (data channel) quality is excessive.

FIG. 19A is a diagram illustrating conceptually a first example of thedistribution of DRC values reported by a communication terminalapparatus according to Embodiment 7 of the present invention, and FIG.19B is a diagram illustrating conceptually a second example of thedistribution of DRC values reported by a communication terminalapparatus according to Embodiment 7 of the present invention. In FIG.19A and FIG. 19B, the horizontal axis shows DRC values and the verticalaxis shows the number of communication terminal apparatuses reportingthose DRC values.

When the DRC value distribution is extremely biased toward the high end(the faster transmission rate end), as shown in FIG. 19A, it can beinferred that cell downlink quality is excessive. That is to say, thebase station apparatus uses more than the necessary transmission powerto perform transmission, and therefore major interference is caused tocommunication terminal apparatuses present in the cell of that basestation apparatus and the cell of another base station apparatus.

In this case, reducing the pilot signal and transmit data transmissionpower results in the DRC value distribution not being extremely biasedtoward the high end (that is, in not having transmit data communicationsto communication terminal apparatuses with good communication qualitypredominate in downlinks), as shown in FIG. 19B. By this means, it ispossible to suppress interference to communication terminal apparatusespresent in the cell of that base station apparatus and the cell ofanother base station apparatus.

The configuration of a base station apparatus according to thisembodiment will be described below. The configuration of a base stationapparatus according to this embodiment is the same as that shown in FIG.15, except that the downlink quality estimation section has thefollowing configuration.

Namely, the downlink quality estimation section calculates the averagevalue and dispersion of DRC values (in other words, pilot signalreception quality in each communication terminal apparatus) using DRCsignals from a DRC signal detector 116, and determines the DRC valuedistribution state based on the results of these calculations. Thisdownlink quality estimation section generates information indicatingtransmission power based on the result of determination of thedistribution state, and outputs this information to a power settingsection 802.

Next, the operation of a base station apparatus according to thisembodiment will be described with further reference to FIG. 20. FIG. 20is a flowchart showing the operation of a base station apparatusaccording to Embodiment 7 of the present invention. Explanations ofoperations in this embodiment identical to operations in Embodiment 5are omitted.

The downlink quality estimation section first calculates the averagevalue and dispersion of DRC values reported by each communicationterminal apparatus. In ST1901, it is determined whether the calculatedaverage value is greater than or equal to a threshold value. When thecalculated average value is greater than or equal to the thresholdvalue, the processing flow proceeds to ST1902; when the calculatedaverage value is less than the threshold value, the processing flowproceeds to ST1904.

In ST1902, it is determined whether the calculated DRC value dispersionis less than or equal to a threshold value. When the calculateddispersion is less than or equal to the threshold value, the processingflow proceeds to ST1903; when the calculated dispersion is greater thanthe threshold value, the processing flow proceeds to ST1904.

In ST1903, the DRC distribution is recognized as being extremely biasedtoward the high end from the fact that the calculated average value isgreater than or equal to the threshold value and the calculateddispersion is less than or equal to the threshold value. Therefore,information is generated indicating that transmission power is to bereduced by, for example, 1 [dB].

In ST1904, on the other hand, when the calculated average value is lessthan the threshold value, or the calculated dispersion is greater thanthe threshold value, it is recognized that the DRC distribution is notextremely biased toward the high end. Furthermore, it is determinedwhether or not the transmission power value at the current point in timeis the normal transmission power value (maximum value). When thetransmission power value at the current point in time is the normaltransmission power value, the processing flow proceeds to ST1901; whenthe transmission power value at the current point in time is less thanthe normal transmission power value, the processing flow proceeds toST1905. In ST1905, information indicating that transmission power is tobe raised by, for example, 1 [dB] is generated.

The information generated in ST1903 or ST1905 is output to the powersetting section 802.

Thus, in this embodiment, by using the distribution of DRC valuesreported by communication terminal apparatuses, it is possible to detectreliably whether or not downlink quality is excessive—that is, whetheror not transmit data communications to communication terminalapparatuses with good communication quality are predominant ondownlinks.

Embodiment 8

In above-described Embodiment 7, the distribution state of DRC values isdetected using the average value and dispersion of DRC values, and usingthe detected distribution state, transmission power is reduced by 1 [dB]when the DRC distribution is biased toward the high end, andtransmission power is raised by just 1 [dB] so as to bring it closer tothe normal transmission power value when the DRC distribution is notbiased toward the high end.

However, even in a situation where the DRC distribution is biased towardthe high end, there is a first case where the DRC distribution is biasedtoward higher DRC values and a second case where the DRC distribution isbiased toward lower DRC values. The optimal transmission power valuereduction amount differs according to whether the first case or thesecond case applies to the DRC distribution state. That is to say,considered from the standpoints of interference to communicationterminal apparatuses in other cells and total throughput, it isdesirable for the optimal reduction amount in the second case to besmaller that the optimal reduction amount in the first case.

Similarly, even in a situation where the DRC distribution is biasedtoward the low end, there is a third case where the DRC distribution isbiased toward lower DRC values and a fourth case where the DRCdistribution is biased toward higher DRC values. The optimaltransmission power value reduction amount differs according to whetherthe third case or the fourth case applies to the DRC distribution state.That is to say, considered from the standpoints of interference tocommunication terminal apparatuses in other cells and total throughput,it is desirable for the optimal increase amount in the third case to begreater that the optimal increase amount in the fourth case.

Thus, in this embodiment, after DRC values for which extreme bias hasoccurred have been determined based on the DRC value distribution statedetected using the average value and dispersion of DRC values,transmission power value control (that is, increase amount or reductionamount control) is performed according to the result of thedetermination.

The configuration of a base station apparatus according to thisembodiment will be described below. The configuration of a base stationapparatus according to this embodiment is the same as that shown in FIG.15, except that the downlink quality estimation section has thefollowing configuration.

Namely, the downlink quality estimation section calculates the averagevalue and dispersion of DRC values (in other words, pilot signalreception quality in each communication terminal apparatus) using DRCsignals from a DRC signal detector 116, and determines the DRC valuedistribution state (specifically, in what DRC values bias has occurred)based on the results of these calculations. This downlink qualityestimation section generates information indicating transmission powerbased on the result of determination of the distribution state, andoutputs this information to a power setting section 802.

Next, the operation of a base station apparatus according to thisembodiment will be described with reference to FIG. 21 and FIG. 22. FIG.21 is a diagram showing an example of the relationship between averageDRC values, dispersion, and transmission power values in a base stationapparatus according to Embodiment 8 of the present invention, and FIG.22 is a flowchart showing the operation of a base station apparatusaccording to Embodiment 8 of the present invention. Detailedexplanations of operations in this embodiment identical to operations inEmbodiment 7 are omitted.

In the downlink quality estimation section, the average value anddispersion of DRC values reported by each communication terminalapparatus are first calculated. Also, information indicatingtransmission power is generated in accordance with the relationshipsshown in FIG. 21, using the calculated average value and dispersion.

Specifically, in ST2101, it is determined whether or not the averagevalue and dispersion of DRC values are in area 6 shown in FIG. 21. Whenthe average value and dispersion are in area 6 (that is, when bias hasoccurred in the highest DRC value), information indicating thattransmission power is to be reduced by 10 [dB] is generated in ST2102,and then the processing flow returns to ST2101. If, on the other hand,the average value and dispersion are not in area 6, the processing flowproceeds to ST2103.

In ST2103, it is determined whether or not the average value anddispersion of DRC values are in area 5. When the average value anddispersion are in area 5 (that is, when bias has occurred in a lower DRCvalue than in the case of area 6), information indicating thattransmission power is to be reduced by 6 [dB] is generated in ST2104,and then the processing flow returns to ST2101. When, on the other hand,the average value and dispersion are not in area 5, the processing flowproceeds to ST2105.

In ST2105, it is determined whether or not the average value anddispersion of DRC values are in area 4. When the average value anddispersion are in area 4 (that is, when bias has occurred in a lower DRCvalue than in the case of area 5), information indicating thattransmission power is to be reduced by 3 [dB] is generated in ST2106,and then the processing flow proceeds to ST2101. When, on the otherhand, the average value and dispersion are not in area 4, the processingflow proceeds to ST2107.

In ST2107, it is determined whether or not the average value anddispersion of DRC values are in area 3. When the average value anddispersion are in area 3 (that is, in the most desirable case in whichbias has not occurred in any DRC value), the processing flow proceeds toST2101 without information indicating that transmission power is to beincreased or reduced being generated. When, on the other hand, theaverage value and dispersion are not in area 3, the processing flowproceeds to ST2108.

In ST2108, it is determined whether or not the average value anddispersion of DRC values are in area 2. When the average value anddispersion are in area 2 (that is, when bias has occurred in a low DRCvalue), it is determined in ST2109 whether or not the transmission powervalue at the current point in time is the normal transmission powervalue. When the transmission power value at the current point in time isthe normal transmission power value, the processing flow returns toST2101 without information indicating that transmission power is to bechanged being generated. When the transmission power value at thecurrent point in time is not the normal transmission power value,information indicating that transmission power is to be raised by 3 [dB]is generated in ST2110, and the processing flow returns to ST2101.

When, on the other hand, the average value and dispersion are not inarea 2, the processing flow proceeds to ST2111.

In ST2111, it is determined whether or not the average value anddispersion of DRC values are in area 1. When the average value anddispersion are in area 1 (that is, when bias has occurred in a lower DRCvalue than in the case of area 2), it is determined in ST2112 whether ornot the transmission power value at the current point in time is thenormal transmission power value. When the transmission power value atthe current point in time is the normal transmission power value, theprocessing flow returns to ST2101 without information indicating thattransmission power is to be changed being generated. When thetransmission power value at the current point in time is not the normaltransmission power value, information indicating that transmission poweris to be raised by 6 [dB] is generated in ST2113, and the processingflow proceeds to ST2101.

Thus, in this embodiment, by determining DRC values for which extremebias has occurred using the average value and dispersion of DRC values,and then performing transmission power control based on the result ofthe determination, it is possible to reduce interference tocommunication terminal apparatuses in other cells and execute animprovement of total throughput at high speed and with high precision.

In a case where the control described in above Embodiment 1 throughabove Embodiment 8 is performed by all base station apparatuses, it ispossible to reduce parts in which the areas of base station apparatusesoverlap, and therefore, although throughput may fall at the instant atwhich transmission power is reduced, taking a long-term view overallsystem throughput can be maximized.

Also, it is possible for the base station apparatuses and communicationterminal apparatuses described in above Embodiment 1 through aboveEmbodiment 8 to be used in combination.

As is clear from the above descriptions, according to the presentinvention it is possible to provide a communication terminal apparatusthat suppresses interference to a communication terminal apparatus thatperforms adaptive modulation communication with another base stationapparatus and a communication terminal apparatus that performs adaptivemodulation communication with the local base station apparatus at thesame time.

This application is based on Japanese Patent Application No. 2000-232270filed on Jun. 26, 2000, Japanese Patent Application No. 2000-204181filed on Jul. 5, 2000, Japanese Patent Application No. 2000-220344 filedon Jul. 21, 2000, and Japanese Patent Application No. 2000-231256 filedon Jul. 31, 2000, entire content of which is expressly incorporated byreference herein.

INDUSTRIAL APPLICABILITY

The present invention is suitable for use in a cellular communicationsystem.

1. A communication terminal apparatus comprising: a reception sectionthat receives a signal transmitted from a base station apparatus; and atransmission section that transmits an indicator indicating a modulationscheme and a power adjustment level in accordance with quality of thereceived signal, wherein: the transmission section transmits (a) theindicator indicating a predetermined modulation scheme and apredetermined power adjustment level when the quality of the receivedsignal is a predetermined value, (b) the indicator indicating amodulation scheme smaller than the predetermined modulation scheme andthe predetermined power adjustment level when the quality of thereceived signal is smaller than the predetermined value, and (c) theindicator indicating the predetermined modulation scheme and a poweradjustment level smaller than the predetermined power adjustment levelwhen the quality of the received signal is larger than the predeterminedvalue.
 2. The communication terminal apparatus according to claim 1,wherein the transmission section transmits the indicator indicating asmaller modulation scheme as the quality of the received signaldecreases.
 3. The communication terminal apparatus according to claim 1,wherein the transmission section transmits the indicator indicating asmaller power adjustment level as the quality of the received signalincreases.
 4. A base station apparatus comprising: a reception sectionthat receives an indicator from a communication terminal apparatus; anda control section that controls a modulation scheme and a poweradjustment level of a signal to be transmitted to the communicationterminal apparatus in accordance with the indicator, wherein: theindicator indicates (a) a predetermined modulation scheme and apredetermined power adjustment level when quality of a previouslytransmitted signal is a predetermined value, (b) a modulation schemesmaller than the predetermined modulation scheme and the predeterminedpower adjustment level when the quality of the previously transmittedsignal is smaller than the predetermined value, and (C) thepredetermined modulation scheme and a power adjustment level smallerthan the predetermined power adjustment level when the quality of thepreviously transmitted signal is larger than the predetermined value. 5.The base station apparatus according to claim 4, wherein the indicatorindicates a smaller modulation scheme as the quality of the transmittedsignal decreases.
 6. The base station apparatus according to claim 4,wherein the indicator indicates a smaller power adjustment level as thequality of the transmitted signal increases.
 7. A radio communicationmethod comprising: a reception step of receiving a signal transmittedfrom a base station apparatus; and a transmission step of transmittingan indicator indicating a modulation scheme and a power adjustment levelin accordance with quality of the received signal, wherein: in thetransmission step, (a) transmitting the indicator indicating apredetermined modulation scheme and a predetermined power adjustmentlevel when the quality of the received signal is a predetermined value,(b) transmitting the indicator indicating a modulation scheme smallerthan the predetermined modulation scheme and the predetermined poweradjustment level when the quality of the received signal is smaller thanthe predetermined value, and (c) transmitting the indicator indicatingthe predetermined modulation scheme and a power adjustment level smallerthan the predetermined power adjustment level when the quality of thereceived signal is larger than the predetermined value.
 8. A radiocommunication method comprising: a reception step of receiving anindicator from a communication terminal apparatus; and a control step ofcontrolling a modulation scheme and a power adjustment level of a signalto be transmitted to the communication terminal apparatus in accordancewith the indicator, wherein: the indicator indicates (a) a predeterminedmodulation scheme and a predetermined power adjustment level whenquality of a previously transmitted signal is a predetermined value, (b)a modulation scheme smaller than the predetermined modulation scheme andthe predetermined power adjustment level when the quality of thepreviously transmitted signal is smaller than the predetermined value,and (c) the predetermined modulation scheme and a power adjustment levelsmaller than the predetermined power adjustment level when the qualityof the previously transmitted signal is larger than the predeterminedvalue.